1. Field of the Invention
This invention relates to a document printed with graphical symbols which encode information. The encoded information is not human readable, but is visible, in the same way that a bar code is visible but not human readable. The term ‘graphical symbol’ means any visible mark which encodes information; it therefore includes glyphs, 2D bar codes and other forms of graphical indicia.
2. Description of the Prior Art
There are many security documents which are communicated between various agencies where the integrity of the documents is a major issue. A prime example is the use of cheques for financial transactions, billions of which are passed between clients and banks and where the risk of fraud is an ever present threat
Security documents have historically been protected by a considerable range of devices. The actual materials from which they are made are difficult for an outsider to obtain or reproduce. There are devices such as holograms or metallic stripes which are intended to provide visual confirmation of integrity. There are machine readable magnetic stripes and, more recently, chips, that can contain information which guarantees authenticity. There is a range of special ink types, some, for instance, with special reflective properties which confuse scanners and make duplication difficult for counterfeiters.
Security documents can be divided into (a) those, such as currency, where the production of counterfeits is the main issue and where security against simple methods of reproduction is required, and (b) those such as cheques where the information contained in the document is the prime consideration. This latter group is the subject of this invention.
There is a need to handle many of these documents automatically using high speed printers and sorters. For this purpose the use of machine readable symbols is crucial. In these circumstances a solution that does not require special materials, or interruption to the workflow, is the requirement.
One system of machine readability from printed documents is the OCR (Optical Character Recognition) system, and this can achieve a high degree of accuracy from standard fonts but tends to fall well short of practical thresholds for handwritten script. A well established alternative solution is the printing of machine readable indicia or other kinds of graphical symbols with fixed formats using the standard printing process.
One method for adding data to printed documents is the use of graphical symbols called ‘glyphs’ (see U.S. Pat. Nos. 5,091,966 and 5,245,165). Glyphs are characters made up from four or five pixels of printed data which give a uniform greyish appearance and would typically be spread in a rectangle across the top of some secure document. This data can be read by scanning and running through an appropriate software program. Glyphs do not vary significantly in appearance across a printed document. They are typically small forward and backward slashes. Glyphs are also always located against a fixed, rectilinear grid. Standardising the shape of glyphs and placing them along a predefined rectilinear grid has been thought necessary for rapid and accurate machine scanning and recognition.
A further method for adding data is the use of 2D bar codes, particularly those in the PDF417 format. These bar codes use a fixed set of symbols and are very robust under such transformations as compression and photocopying.
2D bar codes and glyphs can provide authentication by two main methods. One method is to link the data in the machine embedded form with data that is contained in some other form in the document This other form could be ordinary readable script, or it could be in stylised form as in the MICR (magnetic ink character recognition) line on a cheque. A method is described in Payformance Corporation patent, U.S. Pat. No. 6,170,744 where a one way hash of visually readable information is embedded in a 2D Bar Code. An alternative form of authentication is provided if the embedded data is compared with information held in a database which is indexed by data on the document
One important characteristic of encoding with graphical symbols is that the presence of the carrier of information is wholly overt or clearly apparent. Hence, the glyphs and 2D bar codes are clearly visible, although the information which is encoded in them would need decoding. The visibility of the information carrier is in marked contrast to stegonographic watermarking systems, in which the information carrier is specifically designed not to be readily perceptible; the primary objective of such watermarking schemes is to conceal both the information carrier as well as the information itself. The present invention does not relate to steganographic watermarking systems at all, but instead to systems in which the information carrier is readily perceptible.
As a practical matter, it should be noted that the use of a steganographic watermark to embed information with low visual impact in security documents is not a realistic option. This is because steganographic watermarks typically have a much lower information rate and are difficult to construct in suitable fashion using only the typical laser printer that is available at the time information is embedded into a security document such as a cheque.
There is one major disadvantage with current systems where the information carrier is a pattern of clearly visible graphical symbols feature (i.e. glyphs and 2D bar codes). It is that the feature may spoil the appearance of the document. For many situations, particularly cheques, anything which significantly detracts from the overall appearance of the document is commercially very unattractive. But, prior to the present invention, there has been no alternative to unsightly, conventional glyphs and 2D bar codes.